Heater control system



- April 27, 1937. E. H LOCKWOOD, 2D 2,078,675

HEATER CONTROL SYSTEM Filed 001;. 27,-1934 k INVENTOR Edwin A. Lac/iwood.

' ATTORNEY Patented Apr. 27, 1937 PATENT. OFFICE HEATER ooNraoL SYSTEM Edwin H. Lockwood, II, Mansfield, Ohio, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 27, 1934, Serial No. 750,291

6 Claims.

My invention relates to electric heaters, and particularly to control systems therefor.

An object of my invention is to provide a relatively simple and inexpensive system of control for an electric heater that shall permit of effecting quick initial heating thereof.

Another object or my invention is to provide a thermal controlsystem for a plural-section electric heater that shall be so thermally controlled by the heater as to cause the sections thereof to be traversed by a larger-than-normal current during the heating-up period,- and by a normal current thereafter. a I

Another object of my invention is to provide a 16 thermal control system for an electric heater that shall eilect a quick heating-up thereof to a predetermined heater temperature, and shall effect a change of electrical connections after said temeral kind used in electric stoves or ranges, and a current-limiting resistor together with a threeheat snap-switch of the usual kind now employed to vary the electrical connections to the respective sections, and add to said system a plural position, plural-contact electromagnetic switch and a thermostatic switch subjected to heat from the heating unit and having a relatively large temperature differential of operation between its two opposed limiting operative positions.

In the single sheet of drawings:

Figure 1 is a view in vertical section, taken through one form of plural-section electric heating unit with which the control system embody-' ing my invention may be operatively associated; Fig. 2 is a diagram showing the connections of the system embodying my invention during the heating-up period of operation;

Fig. 3 is a view similar to Fig. 2, but showing the connections after the heater temperature has reached a certain value;

Fig. 4 is a diagram showing the connections as modified by the three-heat switch to obtain an intermediate temperature;

Fig. 5 is a diagram showing the connections as modified by the three-heat switch to obtain a low temperature; and,

Fig. 6 is a diagram showing the connections of the system when the same has been deenergized by the three-heat switch.

Increasing demands have been made by users of electric heating and,- particularly, cooking appliances for a quicker temperature rise in the heating element, so that such heating elements may be comparable, as to speed of heating-up, with the ordinary gas heater. It is obvious that one method of increasing the rate of initial heating of an electric heating unit is to reduce its thermal mass, so that a relatively small amount only of the heat will be stored therein. Another method of increasing the initial temperature rise in a given time is to so arrange the connections or to provide a control system for the electrical heater as will cause a larger-than-normal currentvalue to traverse the heater during the initial period of operation until a certain temperature has been reached whereafter the normal current or a selectively controlled current will be caused to traverse the heating unit.-

Referring first to Fig. 1 of the drawing, I have there shown one form of heating unit ll, particularly adapted to be used in cooking appliances and comprising an upper relatively thin sheet metal plate l3, a lower thin sheet metal plate I5, each of these'plates having cooperating substantially semi-circular grooves I'l therein, any desired number of such grooves being provided, and the grooves in the plates being so located as to cooperate with each other substantially as shown in Fig. 1 of the drawing. A plural section heating element comprising helically wound resistor wire i9 is insulatedly located in the substantially circular grooves, the electric insulating material 2| being located around said helix I9, so as toextend between it and the inner walls of the semi-circular grooves ll of the respective plates. I provide two sections 23 and 25 of resistor wire 19 (see Fig. 2 of the drawing) for a purpose that will hereinafter appear, such sections being now well known in the art.

The granular electric insulating material 2| may be generated by the method disclosed and claimed in United States Reissue Patent 16,340 to C. B. Backer. This method may be briefly described as follows. The resistor helix I9 is surrounded by an open helix of initially metallic magnesium ribbon which is subjected to the action of high temperature steam whereby the initially metallic magnesium is converted into magnesium hydroxide, which is then heated to change the hydroxide into an oxide.

The two plates i3 and I5 may be spot welded,

2 amen as shown at 21, at a plurality of points over the periphery of the two plates and between the grooves and outside of the same, and the upper plate may have its outer peripheral edge returnbent tightly around and over the periphery of the lower plate to provide a strong substantially flat heating unit. While no terminals have been shown, these have been omitted for the sake of clearness, and it is to be understood that-a plu- 10 rality of such terminals are provided in a manner 3|, and a nut 33 thereon.

The bottom wall of casing 23 is provided with an opening 35 therein at one side thereof to receive a thermostat 3! which thermostat may comprise a suitable base 33, which may be made of electric-insulating material, having a pair of contact terminals 4| and 43 mounted thereon, and a snap-acting bimetal disc 45 supported from the base by a stud 41 extending centrally of the disc to loosely support the same, and permit it to 2 take either one of two opposed hunting positions,

one of which is shown in Fig. 1 of the drawing, where the circuit controlled by the thermostat is closed. The design and construction of the bimetal disc 45 is that disclosed and claimed in 30 Patent No. 1,448,240 to-J. A. Spencer. The main characteristic of such a bimetal disc is that it has a relatively large temperature diiferential of operation, that is, the temperature of the ambientmedium aflecting the bimetal disc must vary 5 through a large value before the disc will move from one of its operative positions to its other 4 operative position. For illustrative purposes, I

may mention that I prefer to have the disc 45 so designed and constructed that the temperature at which it will move from the position shown in Fig. l of the drawing to its open position, where it will be dished in the other direction, may be on the order of 350 to 400, and that it will not reclose until the temperature drops to a value comparable to or on the order of room temperature, or only slightly above such value, that is, F. to 200 F.

Referring now to Fig. 2 of the drawing, I have there illustrated the two sections 23 and 25 of the heater schematically, and have also shown an electromagnetic switch 33 comprising an energizing coil 5|, a core 53 energizable thereby, two contact bridging members 55 and 51, moved by the core 53 into either one of two opposed limiting positicms. The members 55 and 51 when moved to their upper positions, engage fixed contact members 58 and 53 and 60 and BI, respectively, and may engage contact members 62 and 83 and 63 and 65, respectively, when in their lowermost position.

I provide further a current limiting resistor or reactor 1 l, the connections of which in the circuit will be hereinafter set forth in detail. I provide further a three-heat snap-switch 13 of a kind now well known in the art and embodying a plurality of superposed, coaxial contact members I3, 11 and I3 mountedon a common shaft 30 and cooperating with a plurality of fixed contact terminals, the whole structure being effective to vary the connections of the two sections 23 and 23 of the electrical heater to an electrical supply circuit to obtain threediflerent'degrees of heat, as well as to fully deenergize the heating units, in a manner well known in the art, and as will be hereinafter set forth. I provide, preferably, but

- ill! of switch 13.

not necessarily, a three-wire supply circuit in cluding supply circuit conductors ll, 33 and II, there being a voltage difference of volts between neutral conductor 33 and the outer conductors 3| and 33, respectively, while a potential difference of 220 volts may exist between conductors 3| and 35. While I have mentioned certain potential diflerence, I do not desire to be limited thereto since these are mentioned only for the purposes of setting forth the general characteristics of the supply circuit.

Supply circuit conductor II is connected by a conductor 31 to a contact member 33 of switch I3. A conductor 3| connects terminal 33 and terminal 33 of switch 13 to the outer terminal of section 23 and a conductor 31 connects conductor 3| to terminal 33 of contactor 33. The inner terminals of the two sections 23 and 23 are connected together and their Junction is connected by conductor 33 to the two fixed-terminals 33 and 62 of switch 43. One contact member of the thermostat 31 is connected to conductor 3|,- while the other terminal thereof is connected through a conductor lfll to one terminal of coil 3! while the other terminal thereof is connected by a con-- ductor lll3to terminal 33, which terminal is further connected by a conductor I33 to terminal The outer terminal of section 23 is connected by conductor I33 to terminals 3i and 83 of switch 43. One terminal of the current limiting resistor II is connected by a conductor ill to contact terminal 33 of switch 43, while the other terminal of resistor H is connected by a conductor H3 to supply circuit conductor 35.

A contact terminal H3 on switch 13 is connected by a conductor 1 to supply circuit conductor 33. Supply circuit conductor 36 is con-. nected through a conductor ill to a contact terminal l2l on switch 13, while another contact terminal I23 is connected by a conductor I23 to terminal 33 of electromagnetic switch 33.

Fig. 2 of the drawing shows the electrical connections as they exist at the time of initial energization of the heating element comprising the sections 23 and 23 as by an operator having moved the snap-switch 13 so that the respective fixed and movable contact members thereof occupy the positions shown in Fig. 2 of the drawing. Since the temperature of theheating element II is relatively low. disc 33 will be in its closed position. substantially as shown in Fig. l of the drawing, so that it will establish an energizing circuit through coil II which may be traced as follows: from supply circuit conductor 3|, through conductor 31, contact terminal 33, connector 1!, terminal 33, conductor 3|, thermostat 31, conductor I3l, coil ll, conductor I03, conductor I33, terminal I31, connector ll, terminal Ill, and through conductor Ill to the neutral supply circuit conductor 33. The electromagnetic switch will, therefore, be in the position in Fig. 2 of the drawing, whereby the following connections are established as regards sections 23 and 23 of the heating-unit H: from supply circuit conductor 3 l through conductor 31, terminals 33 and 33 of switch 13, conductor 3| through section 23, conductor 33, contact 33, bridging member II, contact 33, conductor Ill, current limiting resistor II, and conductor 3 to supply circuit conductor ll. At the same time, section 23 is connected in parallel circuit relation with section 23 by a branch circuit including conductor 31, contact 63, a bridging member II, contact 3i, conductor I33, through section 23 and from there through the rest of the circuit hereinbefore set forth including the current limiting resistor H. The two sections 23 and 25 are, therefore, connected in parallel circuit relation relatively to each other and in series with 9. current limiting resistor. It may be here mentioned that I prefer to make the value of the ohmic or inductive resistance of resistor ll such that when the two sections 23 and 25 are connected in parallel and in series with resistor II, the current traversing the two sections or the sections individually may be onthe order of 2 to 3 times normal current value.

This larger-than-normal current causes a relatively quick heating-up of the heating unit ll,-and at a certain temperature which, as has already been set forth, may be on the order of 350 to'400 F., the disc 45' will be moved to its open position, whereby the energizing circuit through coil 5| is interrupted and the bridging members 55 and 51 will be caused to move to their lower operative positions, substantially as shown in Fig. 3 of the drawing.

Briefly, the connections now in effect are such, as will be noted by a study of Fig. 3 of the drawing, that the two sections 23 and 25 of the heating element are connected in series across supply circuit conductors 8| and 85,. the current limiting resistor I l being now out out of circuit or rendered inoperative.

Referring now to Fig. 4 of the drawing, I have there illustrated the position of the respective component parts of the three-heat snap-switch 13, which will be occupied when an operator has moved the snap-switch to a second operative po sition, and a study of the diagram of Fig. 4 will show that section 23 is now connected alone across H volts. As compared to the amount of heat generated by heating unit H when the control system associated therewith was in the positions shown in Fig. 3 of the drawing, an intermediate heat only is obtained since only one of the two sections is energized.

Fig. 5 of the drawing shows the control system when the switch 13 has been moved by an operator to a third energizing position in which, as will be seen by a study of this figure of the drawing, the two sections 23 and 25 are connected in series circuitrelation relatively to each other and across supply circuit conductors 83 and 85. This provides what is usually called a low heat.

Fig. 6 of the drawing shows the connections of the control system, and particularly of thesnapswitch 13 when the snap-switch has been moved to a position to completely deenergize the heating unit comprising the sections 23 and 25.

The control system embodying my invention thus provides means including a plural contact, plural position relay or electromagnet switch controlled by a thermostat having a large temperature differential of operation, whereby the two sections of a plural switch heating unit are electrically connected in parallel with each other, and in series with a current limiting resistor to thereby efiect the expenditure of more than the normal amount of electric energy in the heating unit during the heating-up period, whereby said period is greatly decreased in length. Upon the heating unit reaching a predetermined temperature, the thermostat effects a change in the electrical connections, whereby current of a normal value is causedto' traverse the heating unit, the electrical connections to the energizing circuit remaining the same, or in other words, the voltage applied to the system remains constant.

The thermostatic control element will remain in its open position, once it has been moved into such position, irrespective of a reduction in the temperature of the heating unit itself, such as maybe caused by actuation of the three-heat snap-switch by an operator until the temperature of the heating unit has reached a value substantially on the order of room temperature. This ensures that the control system will not be moved into the positions shown in Fig. 2 of the drawing, that is, to cause a larger-than-normal current to traverse the heating unit until the heating unit is again to be energized under such conditions that it will cause a quick heating-up thereof.

Various modifications may be made in thedevice embodying my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art or are set forth in the appended claims.

I claim as my invention:

1. In a control system for a plural section heating unit, in combination, an auxiliary resistor, a plural contact plural position relay and a thermostat located in heat receiving relation to the heating unit and controlling the relay to connect the sections of the heating unit in parallel, and in series with the auxiliary resistor, when starting cold and to connect the sections in series and to cut the auxiliary resistor out of circuit when a certain temperature of the heating unit is reached and to prevent reconnection in parallel until the heating unit has cooled to substantially room temperature.

2. A'control system for a plural section heating unit comprising, in combination, with said heating unit, a three heat manually-actuable switch controlling the connections of the heating unit to an energizing circuit, a plural contact electromagnetic relay, a thermostat located in heat receiving relation to the heating unit, a current,v

limiting auxiliary resistor and electric connec tions between the heating unit, thermostat, relay coil, relay contacts, switch and auxiliary resistor to cause the sections of the heating unit to be connected in parallel with each other and in series with the auxiliary resistor to an energizing circuit as long as the temperature is below a certain maximum value and to cause the sections to be connected in series circuit with each other and to an energizing circuit at all temperatures above said maximum value.

3. A control system comprising, in combination, a plural-section heating unit, a current limiting resistor, a, plural-position plural-contact electromagnetic switch, a thermostat in heat-receiving relation to the heating unit and having a large temperature differential of operation and electric connections between the heating unit, the current limiting resistor, the electromagnetic switch and the thermostat to cause the thermostat to control the electromagnetic switch to connect the sections of the heating unit in parallel with each other and in series with the current limiting re- 'sistor when the system is first energized to effect quick temperature rise 01' the heating unit up to a predetermined temperature value, to then efiect connection or the sections 01' the heating unit in series with each other and to cut the current limiting resistor out of circuit and .to maintain said series connection of the sections of the heating unit down to a value of heating unit temperature on theorder of room temperature.

4. Acontrol system comprising, in combination,

l a plural-section heater, a three-heat switch for the heater, a current-limiting resistor, an electromagnetic switch, a thermostat thermally aflected by the heater and having a large temperature s diilerential of operation and electrical connec-, tions between the heater, the current-limiting resister, the three-heat switch, the electromagnetic switch and the thermostat to cause the thermostat to control the electromagnetic switch to connect the sections of the heater in parallel with each other and in series with the current limiting redstor when first energizing the system, and up to a predetermined value of heater temperature and to then connect the sections in series with each other and cut out the current limiting resister and to maintain said latter connection at all temperatures or the heater down to substantially room temperature and irrespective oi operationoithethreeheat switchtoallbut two of its circuit closing positions.

6. A control system comprising, in combination, a plural section heater, a current limiting resistor, an electromagnetic switch {or the heater. a thermostat thermally controlled by the heater.

v 26 having two opposed limiting positions, and movto almost thesectionsotthe heaterin para-lleLv and the current limiting resistor in series therewith to cause a higher-than-normal current to traverse the heater sections until the heater temperature reaches a certain value and to then con-. trol the electromagnetic switch to connect in circuit the heater sections only, said sections being connected in series, to cause normal current to traverse the sections.

6. A control system comprising, in combination, a plural-section heater, a current limiting resistor, an electromagnetic switch, a thermostat affected by the heater temperature, a supply circuit and electrical connections between the heater sections, the current limiting resistor,the electromagnetic switch, the thermostat and the supply circuit, the thermostat controlling the electromagnetic switch to connect a circuit comprising the sections of the "heater in parallel and the said sections being connected in series, to cause 

